This application is a U.S. National Phase application under 35 U.S.C. xc2xa7371 of PCT Application No. PCT/GB00/03199, filed Aug. 17, 2000, which claims priority under 35 U.S.C. xc2xa7119 from GB Application No. 9919957.2, filed Aug. 23, 1999.
The present invention relates to a class of substituted imidazo-triazine derivatives and to their use in therapy. More particularly, this invention is concerned with substituted imidazo[1,2-d][1,2,4]triazine derivatives which are ligands for GABAA receptors and are therefore useful in the therapy of deleterious mental states.
Receptors for the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), are divided into two main classes: (1) GABAA receptors, which are members of the ligand-gated ion channel superfamily; and (2) GABAB receptors, which may be members of the G-protein linked receptor superfamily. Since the first cDNAs encoding individual GABAA receptor subunits were cloned the number of known members of the mammalian family has grown to include at least six xcex1 subunits, four xcex2 subunits, three xcex3 subunits, one xcex4 subunit, one xcex5 subunit and two xcfx81 subunits.
Although knowledge of the diversity of the GABAA receptor gene family represents a huge step forward in our understanding of this ligand-gated ion channel, insight into the extent of subtype diversity is still at an early stage. It has been indicated that an xcex1 subunit, a xcex2 subunit and a xcex3 subunit constitute the minimum requirement for forming a fully functional GABAA receptor expressed by transiently transfecting cDNAs into cells. As indicated above, xcex4, xcex5 and xcfx81 subunits also exist, but are present only to a minor extent in GABAA receptor populations.
Studies of receptor size and visualisation by electron microscopy conclude that, like other members of the ligand-gated ion channel family, the native GABAA receptor exists in pentameric form. The selection of at least one xcex1, one xcex2 and one xcex3 subunit from a repertoire of seventeen allows for the possible existence of more than 10,000 pentameric subunit combinations. Moreover, this calculation overlooks the additional permutations that would be possible if the arrangement of subunits around the ion channel had no constraints (i.e. there could be 120 possible variants for a receptor composed of five different subunits).
Receptor subtype assemblies which do exist include, amongst many others, xcex11xcex22xcex32, xcex12xcex22/3xcex32, xcex13xcex2xcex32/3, xcex12xcex2xcex31, xcex15xcex23xcex32/3, xcex16xcex2xcex32, xcex16xcex2xcex4 and xcex14xcex2xcex4. Subtype assemblies containing an xcex11 subunit are present in most areas of the brain and are thought to account for over 40% of GABAA receptors in the rat. Subtype assemblies containing xcex12 and xcex13 subunits respectively are thought to account for about 25% and 17% of GABAA receptors in the rat. Subtype assemblies containing an xcex15 subunit are expressed predominantly in the hippocampus and cortex and are thought to represent about 4% of GABAA receptors in the rat.
A characteristic property of all known GABAA receptors is the presence of a number of modulatory sites, one of which is the benzodiazepine (BZ) binding site. The BZ binding site is the most explored of the GABAA receptor modulatory sites, and is the site through which anxiolytic drugs such as diazepam and temazepam exert their effect. Before the cloning of the GABAA receptor gene family, the benzodiazepine binding site was historically subdivided into two subtypes, BZ1 and BZ2, on the basis of radioligand binding studies. The BZ1 subtype has been shown to be pharmacologically equivalent to a GABAA receptor comprising the xcex11 subunit in combination with a xcex2 subunit and xcex32. This is the most abundant GABAA receptor subtype, and is believed to represent almost half of all GABAA receptors in the brain.
Two other major populations are the xcex12xcex2xcex32 and xcex13xcex2xcex32/3 subtypes. Together these constitute approximately a further 35% of the total GABAA receptor repertoire. Pharmacologically this combination appears to be equivalent to the BZ2 subtype as defined previously by radioligand binding, although the BZ2 subtype may also include certain xcex15-containing subtype assemblies. The physiological role of these subtypes has hitherto been unclear because no sufficiently selective agonists or antagonists were known.
It is now believed that agents acting as BZ agonists at xcex11xcex2xcex32, xcex12xcex2xcex32 or xcex13xcex2xcex32 subunits will possess desirable anxiolytic properties. Compounds which are modulators of the benzodiazepine binding site of the GABAA receptor by acting as BZ agonists are referred to hereinafter as xe2x80x9cGABAA receptor agonistsxe2x80x9d. The xcex11-selective GABAA receptor agonists alpidem and zolpidem are clinically prescribed as hypnotic agents, suggesting that at least some of the sedation associated with known anxiolytic drugs which act at the BZ1 binding site is mediated through GABAA receptors containing the xcex11 subunit. Accordingly, it is considered that GABAA receptor agonists which interact more favourably with the xcex12 and/or xcex13 subunit than with xcex11 will be effective in the treatment of anxiety with a reduced propensity to cause sedation. Also, agents which are antagonists or inverse agonists at xcex11 might be employed to reverse sedation or hypnosis caused by xcex11 agonists.
The compounds of the present invention, being selective ligands for GABAA receptors, are therefore of use in the treatment and/or prevention of a variety of disorders of the central nervous system. Such disorders include anxiety disorders, such as panic disorder with or without agoraphobia, agoraphobia without history of panic disorder, animal and other phobias including social phobias, obsessive-compulsive disorder, stress disorders including post-traumatic and acute stress disorder, and generalized or substance-induced anxiety disorder; neuroses; convulsions; migraine; depressive or bipolar disorders, for example single-episode or recurrent major depressive disorder, dysthymic disorder, bipolar I and bipolar II manic disorders, and cyclothymic disorder; psychotic disorders including schizophrenia; neurodegeneration arising from cerebral ischemia; attention deficit hyperactivity disorder; and disorders of circadian rhythm, e.g. in subjects suffering from the effects of jet lag or shift work.
Further disorders for which selective ligands for GABAA receptors may be of benefit include pain and nociception; emesis, including acute, delayed and anticipatory emesis, in particular emesis induced by chemotherapy or radiation, as well as post-operative nausea and vomiting; eating disorders including anorexia nervosa and bulimia nervosa; premenstrual syndrome; muscle spasm or spasticity, e.g. in paraplegic patients; and hearing loss. Selective ligands for GABAA receptors may also be effective as pre-medication prior to anaesthesia or minor procedures such as endoscopy, including gastric endoscopy.
The present invention provides a class of imidazo-triazine derivatives which possess desirable binding properties at various GABAA receptor subtypes. The compounds in accordance with the present invention have good affinity as ligands for the xcex12 and/or xcex13 subunit of the human GABAA receptor. The compounds of this invention may interact more favourably with the xcex12 and/or xcex13 subunit than with the xcex11 subunit. Desirably, the compounds of the invention will exhibit functional selectivity in terms of a selective efficacy for the xcex12 and/or xcex13 subunit relative to the xcex11 subunit.
The compounds of the present invention are GABAA receptor subtype ligands having a binding affinity (Ki) for the xcex12 and/or xcex13 subunit, as measured in the assay described hereinbelow, of 100 nM or less, typically of 50 nM or less, and ideally of 10 nM or less. The compounds in accordance with this invention may possess at least a 2-fold, suitably at least a 5-fold, and advantageously at least a 10-fold, selective affinity for the xcex12 and/or xcex13 subunit relative to the xcex11 subunit. However, compounds which are not selective in terms of their binding affinity for the xcex12 and/or xcex13 subunit relative to the xcex11 subunit are also encompassed within the scope of the present invention; such compounds will desirably exhibit functional selectivity in terms of a selective efficacy for the xcex12 and/or xcex13 subunit relative to the xcex11 subunit.
The present invention provides a compound of formula I, or a salt or prodrug thereof: 
wherein
Y represents hydrogen, C1-6 alkyl or C3-7 cycloalkyl;
Z represents C1-6 alkyl, C3-7 cycloalkyl, C4-7 cycloalkenyl, C6-8 bicycloalkyl, aryl, C3-7 heterocycloalkyl, heteroaryl or di(C1-6)alkylamino, any of which groups may be optionally substituted;
R1 represents C3-7 cycloalkyl, phenyl, furyl, thienyl or pyridinyl, any of which groups may be optionally substituted; and
R2 represents C3-7 cycloalkyl(C1-6)alkyl, aryl(C1-6)alkyl or heteroaryl(C1-6)alkyl, any of which groups may be optionally substituted.
The present invention also provides a compound of formula I as depicted above, or a salt or prodrug thereof, wherein Y represents hydrogen or C1-6 alkyl; and Z, R1 and R2 are as defined above.
The groups Z, R1 and R2 may be unsubstituted, or substituted by one or more, suitably by one or two, substituents. In general, the groups Z, R1 and R2 will be unsubstituted or monosubstituted. Examples of optional substituents on the groups Z, R1 and R2 include C1-6 alkyl, aryl(C1-6)alkyl, pyridyl(C1-6)alkyl, halogen, halo(C1-6)alkyl, cyano, cyano(C1-6)alkyl, hydroxy, hydroxymethyl, C1-6 alkoxy, C3-7 cycloalkyl(C1-6)alkoxy, C3-7 cycloalkoxy, amino(C1-6)alkyl, di(C1-6)alkylamino(C1-6)alkyl, di(C1-6)alkylaminocarbonyl(C1-6)alkyl, N-(C1-6)alkylpiperidinyl, pyrrolidinyl(C1-6)alkyl, piperazinyl(C1-6)alkyl, morpholinyl(C1-6)alkyl, di(C1-6)alkylmorpholinyl(C1-6)alkyl and imidazolyl(C1-6)alkyl. Representative substituents include C1-6 alkyl, aryl(C1-6)alkyl, halogen, cyano, hydroxy, hydroxymethyl, C1-6 alkoxy and C3-7 cycloalkyl(C1-6)alkoxy. Particular substituents include C1-6 alkyl and halogen, specifically methyl, ethyl, fluoro or chloro, and especially methyl, fluoro or chloro.
As used herein, the expression xe2x80x9cC1-6 alkylxe2x80x9d includes methyl and ethyl groups, and straight-chained or branched propyl, butyl, pentyl and hexyl groups. Particular alkyl groups are methyl, ethyl, n-propyl, isopropyl, tert-butyl and 1,1-dimethylpropyl. Derived expressions such as xe2x80x9cC1-6 alkoxyxe2x80x9d are to be construed accordingly.
Typical C3-7 cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
The expression xe2x80x9cC3-7 cycloalkyl(C1-6)alkylxe2x80x9d as used herein includes cyclopropylmethyl, cyclobutylmethyl, cyclopentylmethyl and cyclohexylmethyl.
Typical C4-7 cycloalkenyl groups include cyclobutenyl, cyclopentenyl and cyclohexenyl.
Typical C6-8 bicycloalkyl groups include bicyclo[2.1.1]hexyl and bicyclo[2.2.1]heptyl.
Typical aryl groups include phenyl and naphthyl, preferably phenyl.
The expression xe2x80x9caryl(C1-6)alkylxe2x80x9d as used herein includes benzyl, phenylethyl, phenylpropyl and naphthylmethyl.
Suitable heterocycloalkyl groups include azetidinyl, pyrrolidinyl, piperidinyl, piperazinyl, morpholinyl and thiomorpholinyl groups.
Suitable heteroaryl groups include pyridinyl, quinolinyl, isoquinolinyl, pyridazinyl, pyrimidinyl, pyrazinyl, quinoxalinyl, furyl, benzofuryl, dibenzofuryl, thienyl, benzthienyl, pyrrolyl, indolyl, pyrazolyl, indazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl, imidazolyl, benzimidazolyl, oxadiazolyl, thiadiazolyl, triazolyl and tetrazolyl groups.
The expression xe2x80x9cheteroaryl(C1-6)alkylxe2x80x9d as used herein includes furylmethyl, furylethyl, thienylmethyl, thienylethyl, pyrazolylmethyl, oxazolylmethyl, oxazolylethyl, isoxazolylmethyl, thiazolylmethyl, thiazolylethyl, imidazolylmethyl, imidazolylethyl, benzimidazolylmethyl, oxadiazolylmethyl, oxadiazolylethyl, thiadiazolylmethyl, thiadiazolylethyl, triazolylmethyl, triazolylethyl, tetrazolylmethyl, tetrazolylethyl, pyridinylmethyl, pyridinylethyl, pyridazinylmethyl, pyrimidinylmethyl, pyrazinylmethyl, quinolinylmethyl, isoquinolinylmethyl and quinoxalinylmethyl.
The term xe2x80x9chalogenxe2x80x9d as used herein includes fluorine, chlorine, bromine and iodine, especially fluorine or chlorine.
For use in medicine, the salts of the compounds of formula I will be pharmaceutically acceptable salts. Other salts may, however, be useful in the preparation of the compounds according to the invention or of their pharmaceutically acceptable salts. Suitable pharmaceutically acceptable salts of the compounds of this invention include acid addition salts which may, for example, be formed by mixing a solution of the compound according to the invention with a solution of a pharmaceutically acceptable acid such as hydrochloric acid, sulphuric acid, methanesulphonic acid, fumaric acid, maleic acid, succinic acid, acetic acid, benzoic acid, oxalic acid, citric acid, tartaric acid, carbonic acid or phosphoric acid. Furthermore, where the compounds of the invention carry an acidic moiety, suitable pharmaceutically acceptable salts thereof may include alkali metal salts, e.g. sodium or potassium salts; alkaline earth metal salts, e.g. calcium or magnesium salts; and salts formed with suitable organic ligands, e.g. quaternary ammonium salts.
The present invention includes within its scope prodrugs of the compounds of formula I above. In general, such prodrugs will be functional derivatives of the compounds of formula I which are readily convertible in vivo into the required compound of formula I. Conventional procedures for the selection and preparation of suitable prodrug derivatives are described, for example, in Design of Prodrugs, ed. H. Bundgaard, Elsevier, 1985.
Where the compounds according to the invention have at least one asymmetric centre, they may accordingly exist as enantiomers. Where the compounds according to the invention possess two or more asymmetric centres, they may additionally exist as diastereoisomers. It is to be understood that all such isomers and mixtures thereof in any proportion are encompassed within the scope of the present invention.
Typical values for the substituent Y include hydrogen, methyl, ethyl and cyclopropyl, especially hydrogen or methyl. In one embodiment, Y represents hydrogen. In another embodiment, Y represents methyl. In a further embodiment, Y represents ethyl. In a still further embodiment, Y represents cyclopropyl.
Examples of suitable values for the substituent Z include methyl, ethyl, isopropyl, tert-butyl, 1,1-dimethylpropyl, methyl-cyclopropyl, cyclobutyl, methyl-cyclobutyl, cyclopentyl, methyl-cyclopentyl, cyclohexyl, cyclobutenyl, bicyclo[2.1.1]hex-1-yl, bicyclo[2.2.1]hept-1-yl, phenyl, fluorophenyl, chlorophenyl, pyrrolidinyl, methyl-pyrrolidinyl, piperidinyl, morpholinyl, thiomorpholinyl, pyridinyl, furyl, thienyl, chloro-thienyl and diethylamino.
Illustrative values of Z include cyclobutyl, cyclopentyl, cyclohexyl, phenyl, fluorophenyl, chlorophenyl and thienyl.
Representative values of Z include cyclobutyl, cyclopentyl, phenyl and chlorophenyl.
In a particular embodiment, the substituent Z represents C3-7 cycloalkyl, either unsubstituted or substituted by C1-6 alkyl, especially methyl. Favourably, Z represents cyclobutyl, cyclopentyl or cyclohexyl, specifically cyclobutyl or cyclopentyl, especially cyclobutyl.
In another embodiment, Z represents tert-butyl.
In a further embodiment, Z represents phenyl.
In a still further embodiment, Z represents fluorophenyl, especially 2-fluorophenyl.
In a yet further embodiment, Z represents chlorophenyl, especially 3-chlorophenyl.
In one more embodiment, Z represents thienyl, especially thien-2-yl.
Examples of typical optional substituents on the group R1 include methyl, fluoro and methoxy, especially fluoro.
Representative values of R1 include cyclopropyl, phenyl, methylphenyl, fluorophenyl, difluorophenyl, methoxyphenyl, furyl, thienyl, methyl-thienyl and pyridinyl. More particularly, R1 may represent unsubstituted, monosubstituted or disubstituted phenyl. Most particularly, R1 represents phenyl, fluorophenyl or difluorophenyl.
Suitably, R2 represents aryl(C1-6)alkyl or heteroaryl(C1-6)alkyl, either of which groups may be optionally substituted.
Suitable values for the substituent R2 in the compounds according to the invention include cyclohexylmethyl, benzyl, pyrazolylmethyl, isoxazolylmethyl, thiazolylmethyl, thiazolylethyl, imidazolylmethyl, benzimidazolylmethyl, oxadiazolylmethyl, triazolylmethyl, tetrazolylmethyl, pyridinylmethyl, pyridazinylmethyl, pyrimidinylmethyl, pyrazinylmethyl, quinolinylmethyl, isoquinolinylmethyl and quinoxalinylmethyl, any of which groups may be optionally substituted by one or more substituents.
Suitably, R2 represents an optionally substituted triazolylmethyl group.
Examples of suitable optional substituents on the group R2 include C1-6 alkyl, aryl(C1-6)alkyl, pyridyl(C1-6)alkyl, halogen, halo(C1-6)alkyl, cyano, cyano(C1-6)alkyl, hydroxymethyl, C1-6 alkoxy, C3-7 cycloalkyl(C1-6)alkoxy, amino(C1-6)alkyl, di(C1-6)alkylamino(C1-6)alkyl, di(C1-6)alkylaminocarbonyl(C1-6)alkyl, N-(C1-6)alkylpiperidinyl, pyrrolidinyl(C1-6)alkyl, piperazinyl(C1-6)alkyl, morpholinyl(C1-6)alkyl and di(C1-6)alkylmorpholinyl(C1-6)alkyl.
Specific illustrations of particular substituents on the group R2 include methyl, ethyl, n-propyl, benzyl, pyridinylmethyl, chloro, chloromethyl, cyano, cyanomethyl, hydroxymethyl, ethoxy, cyclopropylmethoxy, dimethylaminomethyl, aminoethyl, dimethylaminoethyl, dimethylaminocarbonylmethyl, N-methylpiperidinyl, pyrrolidinylethyl, piperazinylethyl, morpholinylmethyl and dimethylmorpholinylmethyl, particularly methyl or ethyl, especially methyl.
Representative values of R2 include hydroxymethyl-cyclohexylmethyl, cyanobenzyl, hydroxymethyl-benzyl, pyrazolylmethyl, dimethyl-pyrazolylmethyl, methyl-isoxazolylmethyl, thiazolylmethyl, methyl-thiazolylmethyl, ethyl-thiazolylmethyl, methyl-thiazolylethyl, imidazolylmethyl, methyl-imidazolylmethyl, ethyl-imidazolylmethyl, benzyl-imidazolylmethyl, benzimidazolylmethyl, methyl-oxadiazolylmethyl, triazolylmethyl, methyl-triazolylmethyl, ethyl-triazolylmethyl, propyl-triazolylmethyl, benzyl-triazolylmethyl, pyridinylmethyl-triazolylmethyl, cyanomethyl-triazolylmethyl, dimethylaminomethyl-triazolylmethyl, aminoethyl-triazolylmethyl, dimethylaminoethyl-triazolylmethyl, dimethylaminocarbonylmethyl-triazolylmethyl, N-methylpiperidinyl-triazolylmethyl, pyrrolidinylethyl-triazolylmethyl, piperazinylethyl-triazolylmethyl, morpholinylethyl-triazolylmethyl, methyl-tetrazolylmethyl, pyridinylmethyl, methyl-pyridinylmethyl, dimethyl-pyridinylmethyl, ethoxy-pyridinylmethyl, cyclopropylmethoxy-pyridinylmethyl, pyridazinylmethyl, chloro-pyridazinylmethyl, pyrimidinylmethyl, pyrazinylmethyl, quinolinylmethyl, isoquinolinylmethyl and quinoxalinylmethyl.
A favoured value of R2 is methyl-triazolylmethyl.
Another favoured value of R2 is ethyl-triazolylmethyl.
A particular sub-class of compounds according to the invention is represented by the compounds of formula IIA, and salts and prodrugs thereof: 
wherein
Y, Z and R1 are as defined with reference to formula I above;
m is 1 or 2, preferably 1; and
R12 represents aryl or heteroaryl, either of which groups may be optionally substituted.
Suitably, R12 represents phenyl, pyrazolyl, isoxazolyl, thiazolyl, imidazolyl, benzimidazolyl, oxadiazolyl, triazolyl, tetrazolyl, pyridinyl, pyridazinyl, pyrimidinyl, pyrazinyl, quinolinyl, isoquinolinyl or quinoxalinyl, any of which groups may be optionally substituted by one or more substituents.
A particular value of R12 is optionally substituted triazolyl.
Examples of typical substituents on the group R12 include C1-6 alkyl, aryl(C1-6)alkyl, pyridyl(C1-6)alkyl, halogen, cyano, cyano(C1-6)alkyl, hydroxymethyl, C1-6 alkoxy, C3-7 cycloalkyl(C1-6)alkoxy, di(C1-6)alkylamino(C1-6)alkyl, amino(C1-6)alkyl, di(C1-6)alkylaminocarbonyl(C1-6)alkyl, N-(C1-6)alkylpiperidinyl, pyrrolidinyl(C1-6)alkyl, piperazinyl(C1-6)alkyl and morpholinyl(C1-6)alkyl.
Illustrative values of specific substituents on the group R12 include methyl, ethyl, n-propyl, benzyl, pyridinylmethyl, chloro, cyano, cyanomethyl, hydroxymethyl, ethoxy, cyclopropylmethoxy, dimethylaminomethyl, aminoethyl, dimethylaminoethyl, dimethylaminocarbonylmethyl, N-methylpiperidinyl, pyrrolidinylethyl, piperazinylethyl and morpholinylmethyl, particularly methyl or ethyl, especially methyl.
Particular values of R12 include cyanophenyl, hydroxymethyl-phenyl, pyrazolyl, dimethyl-pyrazolyl, methyl-isoxazolyl, thiazolyl, methyl-thiazolyl, ethyl-thiazolyl, imidazolyl, methyl-imidazolyl, ethyl-imidazolyl, benzyl-imidazolyl, benzimidazolyl, methyl-oxadiazolyl, triazolyl, methyl-triazolyl, ethyl-triazolyl, propyl-triazolyl, benzyl-triazolyl, pyridinylmethyl-triazolyl, cyanomethyl-triazolyl, dimethylaminomethyl-triazolyl, aminoethyl-triazolyl, dimethylaminoethyl-triazolyl, dimethylaminocarbonylmethyl-triazolyl, N-methylpiperidinyl-triazolyl, pyrrolidinylethyl-triazolyl, piperazinylethyl-triazolyl, morpholinylethyl-triazolyl, methyl-tetrazolyl, pyridinyl, methyl-pyridinyl, dimethyl-pyridinyl, ethoxy-pyridinyl, cyclopropylmethoxy-pyridinyl, pyridazinyl, chloro-pyridazinyl, pyrimidinyl, pyrazinyl, quinolinyl, isoquinolinyl and quinoxalinyl.
A favoured value of R12 is methyl-triazolyl.
Another favoured value of R12 is ethyl-triazolyl.
A particular subset of the compounds of formula IIA above is represented by the compounds of formula IIB, and pharmaceutically acceptable salts thereof: 
wherein
Y and R1 are as defined with reference to formula I above;
Q represents the residue of a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl or thienyl ring;
R3 represents hydrogen, methyl, fluoro or chloro; and
R4 represents hydrogen, methyl or ethyl.
The present invention also provides a compound of formula IIB as depicted above, or a pharmaceutically acceptable salt thereof, wherein Q represents the residue of a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or phenyl ring; and Y, R1, R3 and R4 are as defined above.
In relation to formula IIB above, R1 suitably represents phenyl, fluorophenyl or difluorophenyl.
In a particular embodiment, Q suitably represents the residue of a cyclobutyl ring. In another embodiment, Q represents the residue of a cyclopentyl ring. In a further embodiment, Q represents the residue of a cyclohexyl ring. In a still further embodiment, Q represents the residue of a phenyl ring. In a yet further embodiment, Q represents the residue of a thienyl ring.
Suitably, R3 represents hydrogen, fluoro or chloro, particularly hydrogen or chloro, especially hydrogen.
Suitably, R4 represents methyl or ethyl, especially methyl.
Another subset of the compounds of formula IIA above is represented by the compounds of formula IIC, and pharmaceutically acceptable salts thereof: 
wherein
Y and R1 are as defined with reference to formula I above; and
Q, R3 and R4 are as defined with reference to formula IIB above.
Specific compounds within the scope of the present invention include:
3,8-diphenyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
8-(2-fluorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-3-phenyl-imidazo[1,2-d][1,2,4]triazine;
8-(2-fluorophenyl)-2-(1-methyl-1H-[1,2,4]triazol-3-ylmethoxy)-3-phenyl-imidazo[1,2-d][1,2,4]triazine;
8-(2,5-difluorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-3-phenylimidazo[1,2-d][1,2,4]triazine;
8-(4-fluorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-3-phenyl-imidazo[1,2-d][1,2,4]triazine;
8-(2,6-difluorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-3-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclobutyl-8-(2-fluorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-imidazo[1,2-d][1,2,4]triazine;
3-(3-chlorophenyl)-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenyl-imidazo[1,2-d][1,2,4]triazine;
3-cyclobutyl-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenylimidazo[1,2-d][1,2,4]triazine;
8-(2-fluorophenyl)-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-3-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-5-ethyl-2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-5-ethyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-5-cyclopropyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-phenylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2,6-difluorophenyl)-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3-cyclohexyl-8-(2-fluorophenyl)-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3,8-bis(2-fluorophenyl)-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2,6-difluorophenyl)-2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-5-methylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2-fluorophenyl)-5-methyl-2-(3-methyl-3H-[1,2,3]triazol-4-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2-fluorophenyl)-5-methyl-2-(1-methyl-1H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2-fluorophenyl)-5-methyl-2-(1-methyl-1H-[1,2,3]triazol-4-ylmethoxy)imidazo[l,2-d][1,2,4]triazine;
3-cyclopentyl-2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-(2-fluorophenyl)-5-methylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-8-(2-fluorophenyl)-5-methyl-2-(2-methyl-2H-[1,2,4]triazol-3-ylmethoxy)imidazo[1,2-d][1,2,4]triazine;
3-cyclohexyl-2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-8-(2-fluorophenyl)-5-methylimidazo[1,2-d][1,2,4]triazine;
3-cyclopentyl-2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-5-methyl-8-phenyl-imidazo[1,2-d][1,2,4]triazine;
2-(2-ethyl-2H-[1,2,4]triazol-3-ylmethoxy)-5-methyl-8-phenyl-3-(thien-2-yl)-imidazo[1,2-d][1,2,4]triazine;
and salts and prodrugs thereof.
Also provided by the present invention is a method for the treatment and/or prevention of anxiety which comprises administering to a patient in need of such treatment an effective amount of a compound of formula I as defined above or a pharmaceutically acceptable salt thereof.
Further provided by the present invention is a method for the treatment and/or prevention of convulsions (e.g. in a patient suffering from epilepsy or a related disorder) which comprises administering to a patient in need of such treatment an effective amount of a compound of formula I as defined above or a pharmaceutically acceptable salt thereof The binding affinity (Ki) of the compounds according to the present invention for the xcex13 subunit of the human GABAA receptor is conveniently as measured in the assay described hereinbelow. The xcex13 subunit binding affinity (Ki) of the compounds of the invention is ideally 10 nM or less, preferably 2 nM or less, and more preferably 1 nM or less.
The compounds according to the present invention will ideally elicit at least a 40%, preferably at least a 50%, and more preferably at least a 60%, potentiation of the GABA EC20 response in stably transfected recombinant cell lines expressing the xcex13 subunit of the human GABAA receptor. Moreover, the compounds of the invention will ideally elicit at most a 30%, preferably at most a 20%, and more preferably at most a 10%, potentiation of the GABA EC20 response in stably transfected recombinant cell lines expressing the xcex11 subunit of the human GABAA receptor.
The potentiation of the GABA EC20 response in stably transfected cell lines expressing the xcex13 and xcex11 subunits of the human GABAA receptor can conveniently be measured by procedures analogous to the protocol described in Wafford et al., Mol. Pharmacol., 1996, 50, 670-678. The procedure will suitably be carried out utilising cultures of stably transfected eukaryotic cells, typically of stably transfected mouse Ltkxe2x88x92 fibroblast cells.
The compounds according to the present invention exhibit anxiolytic activity, as may be demonstrated by a positive response in the elevated plus maze and conditioned suppression of drinking tests (cf. Dawson et al., Psychopharmacology, 1995, 121, 109-117). Moreover, the compounds of the invention are substantially non-sedating, as may be confirmed by an appropriate result obtained from the response sensitivity (chain-pulling) test (cf. Bayley et al., J. Psychopharmacol.; 1996, 10, 206-213).
The compounds according to the present invention may also exhibit anticonvulsant activity. This can be demonstrated by the ability to block pentylenetetrazole-induced seizures in rats and mice, following a protocol analogous to that described by Bristow et al. in J. Pharmacol. Exp. Ther., 1996, 279, 492-501.
In order to elicit their behavioural effects, the compounds of the invention will ideally be brain-penetrant; in other words, these compounds will be capable of crossing the so-called xe2x80x9cblood-brain barrierxe2x80x9d. Preferably, the compounds of the invention will be capable of exerting their beneficial therapeutic action following administration by the oral route.
The invention also provides pharmaceutical compositions comprising one or more compounds of this invention in association with a pharmaceutically acceptable carrier. Preferably these compositions are in unit dosage forms such as tablets, pills, capsules, powders, granules, sterile parenteral solutions or suspensions, metered aerosol or liquid sprays, drops, ampoules, auto-injector devices or suppositories; for oral, parenteral, intranasal, sublingual or rectal administration, or for administration by inhalation or insufflation. For preparing solid compositions such as tablets, the principal active ingredient is mixed with a pharmaceutical carrier, e.g. conventional tableting ingredients such as corn starch, lactose, sucrose, sorbitol, talc, stearic acid, magnesium stearate, dicalcium phosphate or gums, and other pharmaceutical diluents, e.g. water, to form a solid preformulation composition containing a homogeneous mixture of a compound of the present invention, or a pharmaceutically acceptable salt thereof When referring to these preformulation compositions as homogeneous, it is meant that the active ingredient is dispersed evenly throughout the composition so that the composition may be readily subdivided into equally effective unit dosage forms such as tablets, pills and capsules. This solid preformulation composition is then subdivided into unit dosage forms of the type described above containing from 0.1 to about 500 mg of the active ingredient of the present invention. Typical unit dosage forms contain from 1 to 100 mg, for example 1, 2, 5, 10, 25, 50 or 100 mg, of the active ingredient. The tablets or pills of the novel composition can be coated or otherwise compounded to provide a dosage form affording the advantage of prolonged action. For example, the tablet or pill can comprise an inner dosage and an outer dosage component, the latter being in the form of an envelope over the former. The two components can be separated by an enteric layer which serves to resist disintegration in the stomach and permits the inner component to pass intact into the duodenum or to be delayed in release. A variety of materials can be used for such enteric layers or coatings, such materials including a number of polymeric acids and mixtures of polymeric acids with such materials as shellac, cetyl alcohol and cellulose acetate.
The liquid forms in which the novel compositions of the present invention may be incorporated for administration orally or by injection include aqueous solutions, suitably flavoured syrups, aqueous or oil suspensions, and flavoured emulsions with edible oils such as cottonseed oil, sesame oil, coconut oil or peanut oil, as well as elixirs and similar pharmaceutical vehicles. Suitable dispersing or suspending agents for aqueous suspensions include synthetic and natural gums such as tragacanth, acacia, alginate, dextran, sodium carboxymethylcellulose, methylcellulose, polyvinyl-pyrrolidone or gelatin.
In the treatment of anxiety, a suitable dosage level is about 0.01 to 250 mg/kg per day, preferably about 0.05 to 100 mg/kg per day, and especially about 0.05 to 5 mg/kg per day. The compounds may be administered on a regimen of 1 to 4 times per day.
The compounds of formula I as defined above may be prepared by a process which comprises reacting a compound of formula III with a compound of formula IV: 
wherein Y, Z, R1 and R2 are as defined above, and L1 represents a suitable leaving group.
The leaving group L1 is suitably a halogen atom, typically chloro.
The reaction between compounds III and IV is conveniently effected by stirring the reactants in a suitable solvent, typically N,N-dimethylformamide, in the presence of a base such as sodium hydride or potassium carbonate.
In another procedure, the compounds of formula I as defined above may be prepared by a process which comprises reacting a compound of formula III as defined above with a compound of formula V:
R2xe2x80x94OHxe2x80x83xe2x80x83(V)
wherein R2 is as defined above; in the presence of triphenylphosphine and diethyl azodicarboxylate.
The reaction is conveniently effected at a temperature in the region of 0xc2x0 C., typically in an inert solvent such as tetrahydrofuran.
The intermediates of formula III above may be prepared by reacting a compound of formula VI with a compound of formula VII: 
wherein Y, Z and R1 are as defined above, L2 represents a suitable leaving group, and X represents a halogen atom, preferably chloro.
The leaving group L2 is suitably a halogen atom, e.g. chloro or bromo.
The reaction between compounds VI and VII may conveniently be accomplished by stirring the reactants in a solvent such as dichloromethane, typically in the presence of pyridine; followed by heating the product thereby obtained with sodium iodide and triethylamine in a solvent such as 1,2-dichloroethane or n-butanol. Alternatively, the reaction between compounds VI and VII may be effected by stirring at 0xc2x0 C. in a suitable solvent, e.g. 1,2-dichloroethane, typically in the presence of approximately one equivalent of an organic base such as triethylamine; followed by heating at reflux in the presence of approximately one further equivalent of triethylamine.
In a further procedure, the compounds of formula I as defined above may be prepared by a process which comprises reacting a compound of formula VIII with a compound of formula IX: 
wherein Y, Z, R1 and R2 are as defined above, and L3 represents a suitable leaving group; in the presence of a transition metal catalyst.
The leaving group L3 is typically a halogen atom, e.g. bromo.
The transition metal catalyst of use in the reaction between compounds VIII and IX is suitably tris(dibenzylideneacetone)-dipalladium(0), in which case the reaction is conveniently effected at an elevated temperature in a solvent such as 1,4-dioxane, typically in the presence of tri-tert-butylphosphine and cesium carbonate.
The intermediates of formula IX in which the leaving group L3 represents bromo may be prepared by brominating a compound of formula X: 
wherein Y, R1 and R2 are as defined above.
The bromination reaction is conveniently effected by treating the appropriate compound of formula X with bromine in a suitable solvent, e.g. a mixture of carbon tetrachloride and chloroform.
The intermediates of formula X may be prepared by reacting a compound of formula IV as defined above with a compound of formula XI: 
wherein Y and R1 are as defined above; under conditions analogous to those described above for the reaction between compounds III and IV.
Alternatively, the intermediates of formula X may be prepared by reacting a compound of formula V as defined above with a compound of formula XI as defined above in the presence of triphenylphosphine and diethyl azodicarboxylate; under conditions analogous to those described above for the reaction between compounds III and V.
The intermediates of formula XI may be prepared by reacting a compound of formula VI as defined above with a compound of formula XII: 
wherein L2 and X are as defined above; under conditions analogous to those described above for the reaction between compounds VI and VII.
The intermediates of formula IV and V above may be prepared by the procedures described in WO 98/04559, or by methods analogous thereto.
Where they are not commercially available, the starting materials of formula VI, VII, VIII and XII may be prepared by methods analogous to those described in the accompanying Examples, or by standard methods well known from the art.
It will be understood that any compound of formula I initially obtained from any of the above processes may, where appropriate, subsequently be elaborated into a further compound of formula I by techniques known from the art. For example, a compound of formula I initially obtained wherein R2 is unsubstituted may be converted into a corresponding compound wherein R2 is substituted, typically by standard alkylation procedures, for example by treatment with a haloalkyl derivative in the presence of sodium hydride and N,N-diethylformamide, or with a hydroxyalkyl derivative in the presence of triphenylphosphine and diethyl azodicarboxylate. Furthermore, a compound of formula I initially obtained wherein the R2 substituent is substituted by a halogen atom, e.g. chloro, may be converted into the corresponding compound wherein the R2 substituent is substituted by a di(C1-6)alkylamino moiety by treatment with the appropriate di(C1-6)alkylamine, typically with heating in a solvent such as 1,4-dioxane in a sealed tube.
Where the above-described processes for the preparation of the compounds according to the invention give rise to mixtures of stereoisomers, these isomers may be separated by conventional techniques such as preparative chromatography. The novel compounds may be prepared in racemic form, or individual enantiomers may be prepared either by enantiospecific synthesis or by resolution. The novel compounds may, for example, be resolved into their component enantiomers by standard techniques such as preparative HPLC, or the formation of diastereomeric pairs by salt formation with an optically active acid, such as (xe2x88x92)-di-p-toluoyl-d-tartaric acid and/or (+)-(di-p-toluoyl-l-tartaric acid, followed by fractional crystallization and regeneration of the free base. The novel compounds may also be resolved by formation of diastereomeric esters or amides, followed by chromatographic separation and removal of the chiral auxiliary.
During any of the above synthetic sequences it may be necessary and/or desirable to protect sensitive or reactive groups on any of the molecules concerned. This may be achieved by means of conventional protecting groups, such as those described in Protective Groups in Organic Chemistry, ed. J. F. W. McOmie, Plenum Press, 1973; and T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, John Wiley and Sons, 1991. The protecting groups may be removed at a convenient subsequent stage using methods known from the art.
The following Examples illustrate the preparation of compounds according to the invention.
The compounds in accordance with this invention potently inhibit the binding of [3H]-flumazenil to the benzodiazepine binding site of human GABAA receptors containing the xcex12 or xcex13 subunit stably expressed in Ltkxe2x88x92 cells.
Reagents
Phosphate buffered saline (PBS).
Assay buffer: 10 mM KH2PO4, 100 mM KCl, pH 7.4 at room temperature.
[3H]-Flumazenil (18 nM for xcex11xcex23xcex32 cells; 18 nM for xcex12xcex23xcex32 cells; 10 nM for xcex13xcex23xcex32 cells) in assay buffer.
Flunitrazepam 100 xcexcM in assay buffer.
Cells resuspended in assay buffer (1 tray to 10 ml).
Harvesting Cells
Supernatant is removed from cells. PBS (approximately 20 ml) is added. The cells are scraped and placed in a 50 ml centrifuge tube. The procedure is repeated with a further 10 ml of PBS to ensure that most of the cells are removed. The cells are pelleted by centrifuging for 20 min at 3000 rpm in a benchtop centrifuge, and then frozen if desired. The pellets are resuspended in 10 ml of buffer per tray (25 cmxc3x9725 cm) of cells.
Assay
Can be carried out in deep 96-well plates or in tubes. Each tube contains:
300 xcexcl of assay buffer.
50 xcexcl of [3H]-flumazenil (final concentration for xcex11xcex23xcex32: 1.8 nM; for xcex12xcex23xcex32: 1.8 nM; for xcex13xcex23xcex32: 1.0 nM).
50 xcexcl of buffer or solvent carrier (e.g. 10% DMSO) if compounds are dissolved in 10% DMSO (total); test compound or flunitrazepam (to determine non-specific binding), 10 xcexcM final concentration.
100 xcexcl of cells.
Assays are incubated for 1 hour at 40xc2x0 C., then filtered using either a Tomtec or Brandel cell harvester onto GF/B filters followed by 3xc3x973 ml washes with ice cold assay buffer. Filters are dried and counted by liquid scintillation counting. Expected values for total binding are 3000-4000 dpm for total counts and less than 200 dpm for non-specific binding if using liquid scintillation counting, or 1500-2000 dpm for total counts and less than 200 dpm for non-specific binding if counting with meltilex solid scintillant. Binding parameters are determined by non-linear least squares regression analysis, from which the inhibition constant Ki can be calculated for each test compound.
The compounds of the accompanying Examples were tested in the above assay, and all were found to possess a Ki value for displacement of [3H]-flumazenil from the xcex12 and/or xcex13 subunit of the human GABAA receptor of 100 nM or less.